The present invention relates to a much improved composting system and to the use of such system for scrubbing gas effluvia such as a high sulfur coal effluent.
Two problems pervading our modern society are the disposal of industrial and municipal wastes and the development of non-air polluting energy production. Relative to the latter problem, the return of industry to the utilization of coal as a principal energy source has considerably heightened efforts at developing non-air polluting techniques for its combustion. While coal reserves are plentiful, the quality thereof vis a vis non-polluting combustibility vary from region to region. Coal quality, from the standpoint of air quality standards, is predicated principally upon the sulfur and nitrogen content thereof. Three basic forms of sulfur are known to exist in coal: i.e. organic sulfur in which the sulfur is covalently bonded to carbon, pyritic sulfur, and sulfate. Governmental regulations prohibit the burning of high sulfur coal, i.e. coal containing greater than about 1.5% to 2% total sulfur, unless the proportion of SO.sub.2 in the resulting effluent is reduced to below acceptance standards. Since it is estimated that approximately 33% of the total available coal in the continental United States exhibits a sulfur content acceptable for combustion without scrubbers, it is important to develop techniques which either improve the coal by lowering the sulfur content thereof prior to combustion or which economically and efficiently scrub the resulting sulfur dioxide in the combustion gas effluent. Further in this regard, 62% of the low sulfur coal reserves in the continental United States are found west of the Mississippi River. Unfortunately, almost 90% of the electric power generating capacity utilizing coal as a heat source is located east of the Mississippi River.
Relative to the first problem noted above, ever increasing growth of industry and population necessarily translates into an ever increasing source of industrial and municipal wastes which must be handled and disposed. The treatment of waste may be observed to vary from simple land-fill techniques to somewhat sophisticated chemical and biochemical conversion methods. With the latter methods, significant capital commitments generally are required and must be justified by virtue of environmental protection requirements and/or the generation of profitable byproducts. Controlled composting procedures are considered to offer significant promise for providing for an improved disposal of biodegradable industrial and municipal wastes while generating a somewhat valuable by-product. The preferred approach to treatment of wastes by biodegradation is one wherein composting is carried out in the thermophilic bacteria-phase at temperatures of about 40.degree.-60.degree. C. At such temperatures, bacteria, otherwise active in the mesophilic phase at lower temperatures, are avoided and noxious odors are not present during the biodegradation process. During the winter months, maintenance of such thermophilic phase temperature can be difficult and even in warmer weather there always is an initial time lag for the waste to reach an appropriate temperature so that the biodegradation process will proceed. Further, near the end of the composting process, the partially cured compost can generate excessive heat which may cause the temperature of the partially cured compost to exceed the maximum temperature which the thermophilic bacteria can tolerate.
Though the above-discussed problems appear to be unrelated, the prior art has attempted to connect them in a somewhat unique, though unsuccessful, fashion. This connection involves the use of soil and cured compost as scrubbers and filters for malodorent gases. In this regard see Bohn, "Soil and Compost Filters of Malodorent Gases", Journal of the Air Pollution Control Association, Vol. 25, No. 9, pp. 953-955 (September, 1975); Bohn, "Compost Scrubbers of Malodorous Air Streams", Compost Science, pp. 15-17 (Winter, 1976); Bohn, "Soil Absorption of Air Pollutants", Journal of Environmental Quality, Vol. 1, No. 4, pp. 372-377 (1972); and Bohn, "Soil Treatment of Organic Waste Gases", Soil for Management of Organic Wastes and Wastewaters, pp. 607-617 (1977). While soil and cured compost filters have proven successful in removing organic molodors from gaseous effluvia, all reported attempts at removing inorganic contaminants (such as, for example, SO.sub.2, H.sub.2 S, NO.sub.x, and the like) have proved unsuccessful. It has been reported that these gases readily are oxidized in the particulate filter to the corresponding acid which acid substantially diminishes the capacity and ability of the compost or soil filter to further absorb such contaminants. The usual solution proposed for this acid build-up problem is to charge lime into the compost for neutralizing the resulting acid. Unfortunately, the porosity and gas permeability of the limed material diminished to such an extent that the filters became useless.
The present invention solves the problems encountered in the prior art and renders an economic and efficient compost filtering operation.